1. Technical Field
The present invention relates to a control valve for controlling a hydraulic pressure. More particularly, the present invention relates to a hydraulic control valve having a filter and also pertains to a plate with a filter for use in a hydraulic control valve.
2. Description of Related Art
FIG. 1 is a sectional view showing a structural example of a conventional hydraulic control valve of the type described above. The hydraulic control valve uses a pressurized working fluid as a control fluid for controlling an actuator such as a cylinder or a motor and also utilizes the pressurized fluid as a drive source for driving a spool. That is, a pressurized fluid led from a fluid supply port 201 in a valve block 200 to a supply port 102 in a valve body 101 of a hydraulic control valve 100 is utilized as a control fluid. At the same time, the pressurized fluid is branched inside the valve body 101 and led to nozzles 106 and 107 of a nozzle flapper mechanism 105 through orifices 103 and 104. Thus, the pressurized fluid is utilized as a pressure source for driving a spool 108.
The fluid flowing toward the nozzles 106 and 107 through the orifices 103 and 104 is once filtered through a filter 109 provided in the valve body 101. The fluid flowing toward the nozzles 106 and 107 passes through narrow gaps, i.e. the orifices 103 and 104 and the nozzles 106 and 107. Therefore, if the gaps are clogged with particles, the normal function of the hydraulic control valve is impaired. To avoid such a problem, the filter 109 is provided in the valve body 101.
The hydraulic control valve having a structure in which the filter 109 is incorporated in the valve body 101 as stated above needs to disassemble the hydraulic control valve 100 to replace the filter 109 when it is clogged with particles or maintenance is carried out, and thus requires a troublesome operation. During the replacement, the hydraulic control valve 100 does not function, and the system using it cannot operate. Therefore, the operating rate of the system is reduced undesirably.
To avoid the reduction in the operating rate of the system, it is conceivable that another hydraulic control valve 100 is prepared, and when the filter 109 is to be replaced, the existing hydraulic control valve is changed with the prepared one to operate the system. In this case, however, the system requires another hydraulic control valve 100. Because there are differences among individual hydraulic control valves, it may be necessary to make readjustment of the system operation and so forth.
There is a hydraulic control valve wherein the filter 109 is detachably provided in the valve body 101 to facilitate the replacement. This arrangement allows the maintenance time to be shortened and is effective in increasing the operating rate of the system. However, because the valve body 101 has a complicated flow passage formed therein, if a filter is further detachably provided in the valve body 101, the number of machining processes necessary for the valve body 101 increases, resulting in an increase in cost. In addition, when the filter 109 is replaced, care must be taken not to allow particles and the like attached to the filter 109 to enter the inside of the valve body 101.
The present invention was made in view of the above-described circumstances. An object of the present invention is to eliminate the above-described problems and to provide a hydraulic control valve designed so that filter replacement is facilitated and the filter replacing operation requires a shortened period of time, and also provide a plate with a filter for use in a hydraulic control valve.
To solve the above-described problem, according to a first feature of the present invention, there is provided a hydraulic control valve having a valve block provided with a plurality of ports and a valve body formed with ports corresponding to the ports of the valve block, wherein a plate is provided between the valve block and the valve body. The plate is formed with a flow passage for providing communication between the ports of the valve block and the ports of the valve body. In addition, a filter is disposed in the flow passage.
According to a second feature of the present invention, the plate in the above-described hydraulic control valve is formed therein with a flow passage for branching a pressurized fluid from the valve block into a control fluid and a pilot fluid. In addition, the valve body is provided with a pilot port for introducing the pilot fluid from the plate, and the filter is provided in a pilot flow passage in the plate.
According to a third feature of the present invention, the valve body in the above-described hydraulic control valve has a hydrostatic bearing for supporting a spool, and the pressurized fluid from the pilot port is introduced into the hydrostatic bearing.
As stated above, a plate is provided between the valve block and the valve body, and a filter is provided in a flow passage in the plate that provides communication between the ports in the valve block and the ports in the valve body. With this arrangement, filter replacement and maintenance can be performed simply by replacing the plate. Thus, the replacing operation is easy and can be completed in a shortened period of time. Therefore, the period of time during which the hydraulic control valve is unavailable for operation can be reduced to a considerable extent. Accordingly, it is possible to increase the operating rate of a system using the hydraulic control valve.
In comparison to the conventional structure in which a filter is incorporated in the valve body, the flow passage in the valve body is simplified, and the valve body can be made compact in size. In addition, the production cost of the valve body can be reduced.
Further, because the system can be operated simply by preparing two low-cost plates with a filter instead of preparing two costly hydraulic control valves, the overall cost of the system can be reduced.
Further, when it is to be replaced or cleaned, the filter can be detached simply by removing the plate, which is independent of the valve body. Therefore, particles attached to the filter can be prevented from entering the inside of the hydraulic control valve.
Further, it is unnecessary to prepare another hydraulic control valve for the purpose of increasing the operating rate of a system using the hydraulic control valve. The operating rate can be increased simply by preparing a plate of simple arrangement that is equipped with a filter.
Further, it is possible to eliminate the influence on the control performance due to the difference among individual hydraulic control valves that would otherwise occur when the hydraulic control valve is replaced with another hydraulic control valve as in the conventional system.
According to a fourth feature of the present invention, another filter is provided in a control flow passage in the plate in the above-described hydraulic control valve, so that filters of different filtration accuracy are provided in the pilot flow passage and the control flow passage.
If different filters are provided in the control flow passage and the pilot flow passage in the plate as stated above, it is possible to independently filter the control fluid flowing through the control flow passage and the pilot fluid flowing through the pilot flow passage.
With the above-described arrangement, it becomes possible to perform not only filtering of the pilot fluid but also filtering of the control fluid. Therefore, the whole system can be improved in reliability. Further, because the pilot fluid and the control fluid can be filtered independently of each other, it is possible to select filters having filtering performance suitable for the pilot fluid and the control fluid.
According to a fifth feature of the present invention, there is provided a plate detachably installed between a valve block and a valve body in a hydraulic control valve, the valve block being provided with a plurality of ports, and the valve body being formed with ports corresponding to the ports of the valve block. The plate is formed with a flow passage for providing communication between the ports of the valve block and the ports of the valve body, and a filter is disposed in the flow passage.
As stated above, the plate installed between the valve block and the valve body is a plate with a filter, that is, a plate having a filter provided in a flow passage formed therein. Thus, a hydraulic control valve with a filter can be constructed simply by installing the plate between the valve block and the valve body.